排序方式： 共有10条查询结果，搜索用时 15 毫秒
1
1.
Targeting seasonal climate forecasts for integration into household level decisions: the case of smallholder farmers in Lesotho 总被引：2，自引：0，他引：2
Gina Ziervogel 《The Geographical journal》2004,170(1):6-21
Seasonal climate forecasts have been promoted as a means to increase the resilience of marginal groups in Africa. The manifestations of this are still to be seen. This paper argues that successful dissemination and adoption of the forecast requires an in-depth profile of the characteristics and needs of user groups. The case study of a mountainous village in southern Lesotho is used to highlight the decisions which one group of marginal users – smallholder farmers – might make in response to the forecast. A participatory role-play exercise explores what information households presently receive and how new climate forecast information could be integrated into seasonal decision making. Results show that there are a number of low-input options available to these farmers for responding to the forecast. Adoption, however, is going to require repeated exposure to the forecast in conjunction with forecast development that is suited to users' needs. The case study is linked back to the larger scale by suggesting paths that seasonal climate forecast development could take if it is to contribute to improving livelihood sustainability among marginal groups. 相似文献
2.
Murphy Sarah J. Washington Richard Downing Thomas E. Martin Randall V. Ziervogel Gina Preston Anthony Todd Martin Butterfield Ruth Briden Jim 《Natural Hazards》2001,23(2-3):171-196
One of the most promising developments for early warning of climate hazards is seasonal climate forecasting. Already forecasts are operational in many parts of the tropics and sub-tropics, particularly for droughts and floods associated with ENSO events. Prospects for further development of seasonal forecasting for a range of climatichazards are reviewed, illustrated with case studies in Africa, Australia, the U.S.A. and Europe. A critical evaluation of the utility of seasonal forecasts centres on vulnerability, communicationchannels, and effective responses. In contrast to short-term prediction, seasonal forecasts raise new issues of preparedness and the use of information. 相似文献
3.
Sedimentological parameters and erosion behaviour of submarine coastal sediments in the south-western Baltic Sea 总被引：9，自引：0，他引：9
The aim of this study was to evaluate the erodibility of submarine coastal sediments for the purpose of modelling sediment dynamics in Mecklenburg Bay, south-western Baltic Sea. Erosion thresholds derived from experiments with a device microcosm on cores of fine sand (n=5, mean grain size=132 µm) and mud (n=5, medium silt size, mean=21 µm), collected at different times of the year, were compared to theoretical critical shear stress velocities based on grain-size measurements. For this purpose, a sedimentological map of natural surface sediments was constructed for the study area. Calculated values for critical shear stress velocities (u* cr-Hjulström ) are 1.2 cm s?1 for fine sand, and 3.75 cm s?1 for cohesive mud. At the mud station, erosion experiments showed an initial transport of the fluffy surface layer (u* cr-initial ) at a mean critical shear stress velocity of 0.39 cm s?1. Initial rolling transport at the fine sand station for single sand grains was recorded at values of 0.5 cm s?1. At higher shear stress velocities, the two sediment types showed diverging erosion behaviour. Measurable erosion (ε>5.0×10?6 kg m?2 s?1) of fine sand starts at a mean critical shear stress velocity (u* cr-erosion ) of 1.15 cm s?1 whereas fluffy surface material on mud cores was eroded at mean u* cr-erosion of 0.62 cm s?1. This indicates that measured erosion thresholds at the fine sand site fit well to calculated critical shear stress velocities whereas calculated erosion thresholds for cohesive mud are roughly 6 times higher than measured values. As erosion behaviour at the mud station was dominated by fluffy surface material, the comparability of measured and calculated threshold values may be reduced. The underlying silt-sized sediment itself was stable due to cohesive effects. This behaviour has to be taken into consideration by using sediment types instead of mean grain sizes for mapping and modelling sediment dynamics. A comparison of the near-bottom hydrodynamic conditions in the study area and experimentally derived critical shear stress velocities suggests that particle transport is controlled by storm events whereas under calm conditions shear stress velocities do not exceed the critical values. 相似文献
4.
Th. Leipe A. Loeffler K. -C. Emeis S. Jaehmlich R. Bahlo K. Ziervogel 《Estuarine, Coastal and Shelf Science》2000,51(6):789
Suspended particulate matter samples were collected from the water column, the bottom nepheloid layer and the ‘ fluffy layer ’ from four stations along a coastal-basin transect in the Pomeranian Bight, western Baltic Sea. Sampling was performed nine times between October 1996 and December 1998 for various analyses, including electron probe x-ray micro analysis for detailed mineralogical investigations.Specific vertical patterns of clay mineral distributions were found. Suspended particulate matter (SPM) in the bottom nepheloid layer and the ‘ fluffy layer ’ overlying sediments was enriched in organic carbon and hydrated three layer clay minerals, whereas the non-aggregated SPM was dominated by quartz and biogenic opal. It appears that separation effects operate during aggregation of mineral particles and organic matter in repeated cycles of resuspension and settling. No clear seasonal variations in the composition of the SPM were found, in spite of high spatial and temporal variability of biological and physical variables. The results suggest that preferential incorporation, possibly aided by microbiological colonization, of hydrated three layer silicates into the organic flocs is a process that occurs under a wide range of conditions. Because aggregates sink faster than individual particles, aggregate formation led to a relative enrichment of illite and smectite in the near-bottom layers. Considering the affinity of organic contaminants and heavy metals to organic matter, the selective removal of aggregated organic matter and hydrated three-layer clay minerals from the water column and enhanced transport in the near-bottom fluffy layer may be a natural cleansing mechanism operating in the shallow waters of the bight. 相似文献
5.
Gina Ziervogel Peter Johnston Margaret Matthew Pierre Mukheibir 《Climatic change》2010,103(3-4):537-554
Water resources, and in particular run-off, are significantly affected by climate variability. At present, there are few examples of how the water management sector integrates information about changing intra-annual climate conditions in a systematic manner in developing countries. This paper, using the case study of Cape Town in the Western Cape, South Africa, identifies processes and products to facilitate increased uptake of seasonal climate forecasts among water resource managers. Results suggest that existing seasonal forecasts do not focus enough on specific users’ needs. In order to increase uptake, forecasts need to include information on the likely impact of precipitation variability on runoff and water availability. More opportunities are also needed for those with climate knowledge to interact with water resource managers, particularly in the developing country context where municipal managers’ capacity is strained. Although there are challenges that need to be overcome in using probabilistic climate information, seasonal forecast information tailored to the needs of water resource planners has the potential to support annual planning and is therefore a means of adapting to climate change. 相似文献
6.
7.
The extent to which marine organic matter is associated with surfaces and the consequences of such associations for organic matter remineralization are the focus of considerable attention. Since extracellular enzymes operating outside microbial cells are required to hydrolyze organic macromolecules to sizes sufficiently small for substrate uptake, the effects of surface interactions–on enzymes as well as on substrates–for hydrolytic activity also require investigation. We used a simplified laboratory system consisting of a free (dissolved) polysaccharide (pullulan) and the same polysaccharide tethered to agarose beads to restrict mobility, plus the corresponding free enzyme (pullulanase) and the same enzyme sorbed to montmorillonite (Mte), to investigate systematically the consequences of surface associations of enzymes and of substrates on hydrolytic activity. Changes in substrate molecular weight were monitored with time to measure the course of enzymatic hydrolysis. Although hydrolysis of free substrate was nearly complete after 2 min incubation with the free enzymes, the sorbed enzymes also effectively hydrolyzed free substrate, and the data suggest that they retained activity longer in solution compared to the free enzymes. Sorbed enzymes progressively hydrolyzed the free substrate from > 50 kD to lower molecular weights during a 24 h incubation, with a final product distribution on average showing only 1.4% and 10.3% of substrate still in the > 50 kD and 10 kD size classes, while 46.6%, 29.3%, and 12.5% of substrate was in the 4 kD, monomer, and free tag size classes, respectively. This product distribution was very similar to that of the free substrate/free enzyme experiment. Tethering the substrate to agarose beads led to lower substrate release (2–3% of total substrate after 98 h incubation) into solution compared to the free substrate case. For tethered substrates, the state of the enzyme (free or sorbed) measurably affected the molecular weight distribution of the hydrolysis products, with free enzymes producing a higher fraction of high molecular weight hydrolysis products (28.7 ± 5.4% of substrate > 50 kD at the end of the incubation) compared to sorbed enzymes (11.6 ± 2.8% of substrate > 50 kD at the end of the incubation.) Tethered substrates were also hydrolyzed in a sediment slurry from surface sediments from Cape Lookout Bight, North Carolina; 0.1% of total substrate was released by enzymes naturally present in 1 cm3 of sediment after 144 h incubation, demonstrating that the enzymes naturally present in marine sediments are also capable of accessing tethered substrates. These investigations suggest that surface associations of enzymes in marine systems may extend the active lifetime of such enzymes, providing an opportunity for hydrolysis over longer periods of time and producing a different size spectrum of hydrolysis products relative to free enzymes. Furthermore, in well-mixed systems, surface-associated enzymes can hydrolyze substrates whose mobility is restricted, highlighting the importance of processes such as resuspension and bioturbation on organic matter remineralization. 相似文献
8.
In order for a scientific innovation to reach a wide audience it needs to travel through diverse networks and be understandable to a variety of people. This paper focuses on networks of stakeholders involved in the diffusion of seasonal climate forecasts. It is argued that understanding stakeholder networks is key to determining the opportunities and barriers to the flow of forecast information, which could enable more focused forecast dissemination. Lesotho is used as a case study where Stakeholder Thematic Networks (STNs) are used as a novel method for investigating forecast dissemination. STNs enable qualitative information to be analysed through semi-quantitative mapping of relationships that enable the networks and scales of linkages to be visualised. This illustrates the types of nodes and channels of seasonal forecast information flow and so enables existing or emerging patterns of dissemination to be uncovered. Sub-networks that exist for purposes other than climate information dissemination are identified as salient sub-networks for focusing development of future forecast dissemination. These existing sub-networks enable stakeholder needs to be addressed and decrease the need for new networks to be established. By using these sub-networks, information relating to climate variability can be mainstreamed into existing development pathways. This is critical to recognise if innovations relating to climate information are to be used to improve climate change adaptation. 相似文献
9.
Extracellular enzyme activities were compared among surface water, bottom water, and sediments of the Delaware Estuary using six fluorescently labeled, structurally distinct polysaccharides to determine the effects of suspended sediment transport on water column hydrolytic activities. Potential hydrolysis rates in surface waters were also measured for the nearby shelf. Samples were taken in December 2006, 6 months after a major flood event in the Delaware Basin that was followed by high freshwater run-off throughout the fall of 2006. All substrates were hydrolyzed in sediments and in the water column, including two (pullulan and fucoidan) that previously were not hydrolyzed in surface waters of the Delaware estuary. At the time of sampling, total particulate matter (TPM) in surface waters at the lower bay, bay mouth, and shelf ranged between 31 mg l−1 and 48 mg l−1 and were 2 to 20 times higher than previously reported. The presence of easily resuspended sediments at the lower bay and bay mouth indicated enhanced suspended sediment transport in the estuary prior to our sampling. Bottom water hydrolysis rates at the two sites affected by sediment resuspension were generally higher than those in surface waters from the same site. Most notably, fucoidan and pullulan hydrolysis rates in bay mouth bottom waters were 22.6 and 6.2 nM monomer h−1, respectively, and thus three and five times higher than surface water rates. Our data suggest that enhanced mixing processes between the sediment and the overlying water broadened the spectrum of water column hydrolases activity, improving the efficiency of enzymatic degradation of high molecular weight organic matter in the water with consequences for organic matter cycling in the Delaware estuary. 相似文献
10.
Climate variability and rural livelihoods: assessing the impact of seasonal climate forecasts in Lesotho 总被引：7，自引：0，他引：7
Climate variability acutely affects rural livelihoods and agricultural productivity, yet it is just one of many stresses that vulnerable rural households have to cope with. A livelihood approach is used to assess the potential role that seasonal climate forecasts might play in increasing adaptive capacity in response to climate variability, using Lesotho as a case study. An examination of the assets and strategies that rural households employ enables a holistic assessment of the impact seasonal forecasts could have on rural livelihoods. This research thereby bridges macro-level variability with local-level impacts and adaptation to provide insight into the dynamics of forecast use and impact among vulnerable groups. 相似文献
1